Electric and hybrid-electric powered vehicles employ a high voltage battery pack to power electric motors that drive the vehicle. These high voltage batteries, sometimes referred to as traction batteries, must be periodically recharged. During periods of nonuse, the vehicle is connected to a source of AC power, such as 110 volt AC. A battery charger located either on-board or off-board the vehicle, converts the 110 volt AC to DC which is used to recharge the traction battery to a desired state of charge.
During normal operation of the vehicle, on-board systems periodically determine the state of charge of the high voltage battery, and in the case of a hybrid electric vehicle, onboard control systems switch from battery power to an alternative power source, such as a fuel cell or IC engine when the state of charge falls below a threshold value. The ability of the high voltage battery pack to hold a full electrical charge is reduced by so called battery “memory.” Battery memory is common in deep discharge batteries which are repeatedly partially discharged and recharged. The memory effect prevents drawing a full charge from a completely charged battery, and also prevents accurate state of charge calculations from being performed on-board the vehicle since a calculated state of charge of a battery suffering from memory infect does not accurately reflect the amount of charge that can be drawn from the battery.
In addition to the high voltage battery pack, the vehicles mentioned above employ a low voltage on-board battery, typically 12 volts, to power the low voltage electrical system on the vehicle. These low voltage batteries, sometimes referred to as SLI batteries (starting, lighting and ignition) must be periodically charged using a battery charger separate from the high voltage battery pack charger. Thus, two battery chargers are normally employed to recharge the on-board battery systems.
Accordingly, there is a need in the art for an improved system for charging both the high voltage and low voltage batteries on vehicles which overcomes the problems discussed above. The present invention is intended to satisfy this need.